1. Field of the Invention
Embodiments of the invention relate to a production of ledeburite tool steels by a powder metallurgical (PM) method, in which PM materials have isotropic, mechanical properties, improved wear resistance and high hardness potential.
2. Discussion of Background Information
Highly alloyed tool steels, which due to their composition solidify ledeburitically, often have locally in the casting state coarse carbides and carbide clusters in the structure which align themselves in band form during a heat deformation of the cast ingot and ultimately form carbide bands dependent on the deformation direction or form a deformation structure. This crystalline structure determines anisotropic property features of the material with respect to the particular direction of stress on the part.
In order to achieve isotropic and improved material properties of highly alloyed tool steels, it is known to apply a powder metallurgical production method which ensures a homogenous distribution of small carbides in the matrix.
In a PM method, there occurs a separating of liquid steel by high-speed streams of gas into small droplets which solidify at a high rate and thereby form fine carbide phases in these. By a subsequent Hot Isostatic Pressing (HIP) of the powder in a capsule, a HIP ingot is produced by sintering which is heat-transformable and advantageously at least has a homogenous distribution of small carbide phases in the material.
Materials produced in this manner are in their mechanical properties to the greatest possible extent isotropic and have good workability but have a reduced hardness potential as a result of the matrix structure. For a person skilled in the art, the term hardness potential refers to the extent of the hardness increase during the annealing of a material that is transformed martensitically from the austenite structure region and has retained austenite.
Furthermore, as was found, PM materials can by comparison be slightly less wear resistant for an identical chemical composition of the alloy, even though equally high carbide phase quantities are present in the matrix during a conventional production.